臺灣博碩士論文加值系統

正交時頻空間(OTFS)調變系統因其在稀疏多路徑的線性時變通道上的優異表現而在無線通訊領域獲得關注。然而，這種系統在接收端的等化與資料決策會需要極高的運算資源，因此研究同時具有優異性能表現與可接受複雜度的接收端符元決策方法是至關重要的。在循環前綴碼式正交時頻空間調變系統(CP-OTFS)中，因為塊狀等化的較低複雜度，我們可以引入迭代符元決策方法來提高系統性能。本論文基於迭代決策反饋混合式等化演算法(IDFHE)，提出了兩種CP-OTFS系統的迭代符元決策方法，能在保有可接受複雜度的同時也提高錯誤率表現。除了一般常討論的線性時變通道，本論文也研究了CP-OTFS系統應用在靜態多路徑通道的可能，以拓展其應用價值。數值分析的結果展示出兩種迭代符元決策方法所帶來的優異性能表現，而計算複雜度的分析也證明了所提出的迭代符元決策方法的可行性。

Orthogonal Time Frequency Space (OTFS) modulation has gained importance in the area of wireless communication networks due to its prominent performance over linear time-varying (LTV) channel exhibiting sparse path delays and Doppler spreads. However, such system experiences tremendously high complexity when performing equalization and data decision at receiver side. Thus, it is crucial to investigate some pragmatic symbol decision methods that encompass acceptable error performance and complexity simultaneously. In cyclic-prefixed-OTFS (CP-OTFS) , since the block-wise equalization is feasible, the iterative symbol decision methods can be introduced to enhance system performance with allowable low-complexity. In this thesis, based on iterative decision-feedback hybrid equalization (IDFHE), an iterative symbol decision method in CP-OTFS, i.e. LM-IDFHE is proposed to improve system performance while maintains realizable complexity. In addition to LTV channel, the iterative symbol decision methods in CP-OTFS over static multipath channel are also developed. It is found that the popular message passing algorithm (MPA) can be incorporated with LM-IDFHE to improve system performance whereas the advantages of both are preserved. The performance results from numerical analysis validate the performance of proposed iterative methods, and the elaboration on computational complexity of each symbol decision method also verifies the feasibility of the proposed symbol decision methods.

Contents
Abstract i
Contents ii
List of Figures iv
List of Tables vii
1 Introduction 1
1.1 Introduction to OTFS System 1
1.2 Review on Symbol Decision Methods in OTFS System 4
1.3 Thesis Motivation 7
2 CP-OTFS System on Static Multipath Channel 10
2.1 System Model 10
2.2 Noniteratively Equalized Symbol Decision Methods and Message Passing Decision 16
2.2.1 Zero-Forcing 18
2.2.2 Linear Minimum Mean Square Error 18
2.2.3 Constrained Least-Square 19
2.2.4 Message Passing Decision 20
2.3 Iterative Decision-Feedback Hybrid Equalization 23
2.3.1 LM-IDFHE Scheme 23
2.3.2 MPA-IDFHE Scheme 26
2.4 Performance Characteristics 29
2.4.1 Random Rician Multipath Channel 30
2.4.2 Effective SINR of LMMSE and CLS Equalizers and Semi-Analytical Bound 31
2.4.3 Bit Error Rate Performance 33
2.4.4 Computational Complexity 36
3 CP-OTFS System on LTV Channel 41
3.1 System Model 42
3.2 Noniteratively Equalized Symbol Decision Methods and Message Passing Decision 48
3.2.1 Linear Minimum Mean Square Error 48
3.2.2 Constrained Least-Square 49
3.2.3 Message Passing Decision 50
3.3 Iterative Decision-Feedback Hybrid Equalization 50
3.4 Performance Characteristics 53
3.4.1 Random Doubly Dispersive Multipath Channel 53
3.4.2 Bit Error Rate Performance 54
3.4.3 Computational Complexity 57
4 Conclusion 61
Bibliography 62

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